[Technical Field]
[0001] The present invention relates to a receiver, an integrated circuit, a receiving method,
and a program, and in particular, to a receiver, an integrated circuit, a receiving
method, and a program that are provided with a demodulator for demodulating a modulation
wave modulated according to orthogonal frequency division multiplexing (OFDM).
[Background Art]
[0002] In various types of current digital communication such as terrestrial digital broadcasting,
IEEE802.11a and the like, orthogonal frequency division multiplexing (OFDM) has been
widely adopted as a transmission method.
[0003] An exemplary OFDM receiver generates reliability information by using calculated
noise power, and utilizes the reliability information to enable high-accuracy error
correction using an LDPC (Low Density Parity Check) code (for example, PTL 1). According
to the technique disclosed in PTL 1, specifically, for noise power calculated from
pilot signals or an OFDM band spectrum, average noise power in a symbol direction
is compared with noise power in each symbol, and in the case where the noise power
in each symbol exceeds a predetermined threshold, it is determined that impulse interference
exists, and a value of the noise power in each symbol is used to generate the reliability
information. On the contrary, in the case where the noise power in each symbol does
not exceed the predetermined threshold, it is determined that the impulse interference
does not exist, and a value of the average noise power in the symbol direction is
used to generate the reliability information. Thereby, even when the noise power locally
increases, proper reliability information can be generated, improving an LDPC decoding
performance. However, PTL 1 fails to mention a specific method of calculating the
noise power in units of symbol.
[0004] Here, the impulse interference means an irregular and random interference signal.
Since impulse noise occurs in an impulse manner from, for example, power-ON/OFF of
household electrical appliances, lighting equipment or automobile ignition, the noise
power locally increases in the symbol in which the impulse noise exists.
[0005] There is a method of estimating the noise power existing in each symbol, which is
necessary for estimating the reliability information (for example, PTL 2). PTL 2 describes
that, in ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) as Japanese
terrestrial digital broadcasting, either or both TMCC (Transmission Multiplexing Configuration
Control) signals and AC (Auxiliary Channel) signals, which are continuously inserted
into a predetermined subcarrier in a time direction are used to estimate the reception
quality.
[Citation List]
[Patent Literature]
[0006]
[PTL 1] European Patent Application Publication No. 2242226
[PTL 2] Japanese Patent No. 3740468
[Summary of Invention]
[Technical Problem]
[0007] The conventional noise power calculation methods disadvantageously depend on a frame
structure. For example, to use the noise power calculation method disclosed in PTL
2, it is need to arrange a signal that can be used to calculate the noise power, such
as a TMCC signal, in each OFDM symbol. Thus, whether or not the noise power calculation
method in PTL 2 can be applied depends on the frame structure of a received signal.
[0008] Therefore, an object of the present invention is to provide a receiver and the like
capable of estimating the reliability information without depending on the received
frame structure.
[Solution to Problem]
[0009] To attain the above-mentioned object, a receiver in accordance with one aspect of
the present invention is a receiver including: a demodulator that demodulates a modulation
wave modulated according to orthogonal frequency division multiplexing (OFDM), the
demodulator including: an interference wave detector that detects that a received
modulation wave which is received by the receiver includes an interference wave when
received power of each sample of the received modulation wave exceeds a threshold,
and upon the detection, executes replacement processing of replacing a received signal
exceeding the threshold with a predetermined value; a first interference wave power
estimation unit configured to estimate interference wave power included in an OFDM
symbol included in the received modulation wave on the basis of the number of samples
that have been subjected to the replacement processing in the OFDM symbol; and a demodulated
data generator that demodulates the received modulation wave by executing demodulation
processing of demodulating the received modulation wave that has been subjected to
the replacement processing by the interference wave detector on the basis of the interference
wave power estimated by the first interference wave power estimation unit, to generate
demodulation data.
[Advantageous Effects of Invention]
[0010] According to the above-mentioned aspect, by calculating the interference power on
the basis of the number of samples exceeding the predetermined threshold during the
OFDM symbol period, the interference power can be calculated without depending on
the received frame structure, thereby enabling stable reception.
[Brief Description of Drawings]
[0011]
[Fig. 1] A block diagram showing a configuration of a receiver in accordance with
First embodiment.
[Fig. 2] A block diagram showing a configuration of a demodulator 11 in accordance
with First embodiment.
[Fig. 3A] A block diagram showing a configuration of an interference wave detector
102 in accordance with First embodiment.
[Fig. 3B] A view showing an example of an interference wave detection signal.
[Fig. 4] A block diagram showing a configuration of a time axis processor 103 in accordance
with First embodiment.
[Fig. 5] A block diagram showing a configuration of an interference wave power estimation
unit 104 in accordance with First embodiment.
[Fig. 6] A block diagram showing a configuration of a reliability estimation unit
108 in accordance with First embodiment.
[Fig. 7] A block diagram showing a configuration of a receiver in accordance with
Second embodiment.
[Fig. 8] A block diagram showing a configuration of a demodulator 21 in accordance
with Second embodiment.
[Fig. 9] A block diagram showing a configuration of an interference wave detector
202 in accordance with Second embodiment.
[Fig. 10] A block diagram showing a configuration of an interference wave power estimation
unit 204 in accordance with Second embodiment.
[Fig. 11] A block diagram showing a configuration of a receiver in accordance with
Third embodiment.
[Fig. 12] A block diagram showing a configuration of a demodulator 31 in accordance
with Third embodiment.
[Fig. 13] A block diagram showing a configuration of an interference wave power estimation
unit 304 in accordance with Third embodiment.
[Fig. 14A] A schematic view showing a transition of CNR in interpolation processing
in channel estimation.
[Fig. 14B] A block diagram showing an example of a configuration of a channel estimation
unit 106.
[Fig. 15] A block diagram showing a configuration of a receiver in accordance with
Fourth embodiment.
[Fig. 16] A block diagram showing a configuration of a demodulator 41 in accordance
with Fourth embodiment.
[Fig. 17] A block diagram showing a configuration of a reliability estimation unit
408 in accordance with Fourth embodiment.
[Fig. 18] A schematic view illustrating a structure of a DVB-T2 frame in a DVB-T2
scheme.
[Fig. 19] A view illustrating relationship between FFT size and the number of P2 symbols.
[Fig. 20] A schematic view illustrating a transmission format (carrier arrangement)
in the DVB-T2 scheme.
[Fig. 21] A schematic view illustrating definition of a carrier interval of SP signals
and a symbol interval.
[Fig. 22] A view illustrating the carrier interval and the symbol interval in each
pilot (SP) pattern.
[Fig. 23] A view illustrating the FFT size, used CP groups, and values used in a modulo
operation.
[Fig. 24] A view illustrating values of the CP groups (CP_g1, CP_g2, CP_g3) for the
pilot patterns.
[Fig. 25] A view illustrating values of the CP group (CP_g4) for the pilot patterns.
[Fig. 26] A view illustrating values of the CP group (CP_g5) for the pilot patterns.
[Fig. 27] A view illustrating values of the CP group (CP_g6) for the pilot patterns.
[Fig. 28] A view illustrating CP carrier positions added in an Extended mode.
[Fig. 29] A schematic view illustrating arrangement of pilot signals in each symbol.
[Fig. 30] A schematic view illustrating a general DVB-T2 receiver.
[Description of Embodiments]
(Findings as a basis for the present invention)
[0012] Prior to description of embodiments of the present invention, digital television
broadcasting adopting an OFDM technology as an example of a system to which the present
invention can be applied will be described with reference to figures.
[0013] The OFDM technology is a method of transmitting a plurality of narrowband digital
modulated signals on multiple frequencies by using a plurality of subcarriers orthogonal
to each other, which is excellent in frequency use efficiency.
[0014] According to the OFDM technology, one symbol section is composed of an effective
symbol section and a guard interval section, for the periodicity in the symbol, some
signals in the effective symbol section are copied and inserted into the guard interval
section. This can reduce the effect of interference between symbols, which is caused
by multipath interference, and has an excellent resistance to the multipath interference.
[0015] In recent years, analog television broadcasting has been stopped in various countries,
and the frequency realignment has become active on a global scale. In Europe, in addition
to SD (Standard Definition) broadcasting adopting DVB-T (Digital Video Broadcasting-Terrestrial),
HD (High Definition) services are in increasingly demand. Under such situations, standardization
of DVB-T2 as the second-generation European terrestrial digital broadcasting is progressing,
and the service has already started in some countries.
[0016] Fig. 18 shows a structure of a DVB-T2 frame in the DVB-T2 scheme. The DVB-T2 frame
is composed of P1 symbols, P2 symbols, and data symbols.
[0017] The P1 symbol has a FFT (Fast Fourier Transform) size of 1 k (= 1024), and contains
information: (1) a format of the P2 symbol and the data symbol (MISO (Multi-Input-Single-Output)
or SISO (Single-Input-Single-Output)), (2) the FFT size of the P2 symbol and the data
symbol, (3) whether or not FEF (Future Extension Frames) is included, and so on.
[0018] The P2 symbol has the same FFT size as the data symbol, and pilots are inserted into
the P2 symbol at regular intervals. In the case of the FFT size of 32 K and the SISO
mode, the P2 pilot exists every six subcarriers. In the case of other parameters,
the P2 pilot exists every three subcarriers. All transmission parameter information
necessary for reception, such as a pilot pattern of the data symbols and a carrier
extended mode (Extended mode or Normal), the number of symbols in each frame, and
modulation method, is added to the P2 symbol. As shown in a table T190 in Fig. 19,
the number of P2 symbols is set for each FFT size of the P2 symbols.
[0019] Fig. 20 shows a transmission format of the DVB-T2 scheme. A horizontal axis represents
an OFDM carrier (frequency) direction, and a vertical axis represents an OFDM symbol
(time) direction. As shown in Fig. 20, an SP (Scattered Pilot) signals is inserted
between data signals at regular intervals in the symbol direction and the carrier
direction. CP (Continual Pilot) signals are successively inserted in particular subcarriers
in the time direction. There are provided eight types of insertion patterns of the
SP signals: PP1 to PP8, and the different patterns have different insertion intervals
in the symbol direction and the carrier direction. As shown in Fig. 21, assuming that
a carrier interval and a symbol interval of carrier positions where the SP signals
exist are Dx and Dy, respectively, the insertion interval Dy in the symbol direction
and an insertion interval (Dx·Dy) in the carrier direction, according to each of the
SP patterns PP1 to PP8 are shown in a table T220 in Fig. 22. The subcarrier position
where the CP signals are inserted is determined depending on the FFT size and the
SP patterns.
[0020] T230 in Fig. 23, and T240, T250, T260, T270 and T280 in Fig. 24 to Fig. 28, respectively,
show positions of the CP signals. Fig. 23 shows which of groups CP_g1 to CP_g6 shown
in Fig. 24 to Fig. 28 is used according to the FFT size. Values obtained by applying
a modulo operation (residue operation) to values shown in Fig. 24 to Fig. 27 by using
K_mod in Fig. 23 represent effective subcarrier numbers in which the CP signals exist.
When the FFT size is 32 k, the modulo operation is not performed, and the values shown
in Fig. 24 to Fig. 27 become the effective subcarrier numbers in which the CP signals
exist as they are. In the case of the Extended mode, the effective subcarrier numbers
shown in Fig. 28 are added. The values in Fig. 28 does not need to be subjected to
the modulo operation.
[0021] Although the CP signals are successively inserted in the time direction, no CP signal
exists in some symbols in an exceptional case. For example, no CP signal exists in
the P2 symbol and a Frame Close symbol. In the case of the transmission format of
SISO, either a normal symbol or the Frame Close symbol is set to the last symbol in
the frame according to combination of the guide interval and the pilot pattern. In
the case of the transmission format of MISO, the Frame Close symbol is set except
for the pattern PP8. Fig. 29 is a schematic view showing a transmission format including
the P2 symbols and the Frame Close symbol. As shown in Fig. 29, more pilots are inserted
into the Frame Close (FC) symbol than pilots inserted into the normal data symbol.
Thereby, in estimating channel characteristics of the pilot signals, the characteristics
can be easily interpolated in the time axis direction. The added pilots other than
the SP signals are called FC (Frame Close) pilots. In the Frame Close symbol, the
FC pilots are added and no CP signal exists. Also in the P2 symbols, since a lot of
P2 pilots exist, no CP signal exists.
[0022] Fig. 30 shows an example of a schematic block diagram of an integrated structure
according to conventional DVB-T2. As shown in Fig. 30, the reception structure according
to the conventional DVB-T2 scheme includes an A/D converter 1002, a time axis processor
1003, an FFT unit 1004, a channel estimation unit 1005, an equalizer 1006, an error
correction unit 1007, and a reliability estimation unit 1008.
[0023] The A/D converter 1002 decodes the P1 symbol from an A/D (analog-digital) converted
signal.
[0024] The time axis processor 1003 synchronizes carrier frequencies and sampling frequencies
of the P2 symbol and the data symbol.
[0025] The FFT unit 1004 performs FFT for conversion into a signal along the frequency axis.
[0026] The channel estimation unit 1005 estimates channel characteristics on the basis of
the SP signal included in the signal that has been subjected to FFT.
[0027] The equalizer 1006 performs distortion compensation (equalization) of the signal
that has been subjected to FFT.
[0028] The error correction unit 1007 performs error correction to decode data.
[0029] The reliability estimation unit 1008 estimates the reliability information in channel
estimation. The estimated reliability information is used for the error correction
in the error correction unit 1007.
[0030] The DVB-T2 employs an LDPC (Low Density Parity Check) code as an error correction
code. To decode the LDPC code, the reliability information representing the reliability
of data is necessary for weighting of log likelihood ratio. The reliability information
is estimated based on signal power estimated in each symbol and noise power including
the effect of thermal noise or interference wave. To improve the error correction
performance in LDPC decoding, it is critically important to appropriately generate
an integrated propagation state as the reliability information.
[0031] For example, PTL discloses a method of assessing the noise power existing in each
symbol, which is necessary for estimating the reliability information. According to
the technology disclosed in PTL 2, in the ISDB-T (Integrated Services Digital Broadcasting-Terrestrial)
as the Japanese terrestrial digital broadcasting, the reception quality is assessed
using at least either TMCC (Transmission Multiplexing Configuration Control) signals
or AC (Auxiliary Channel) signals that are successively inserted into predetermined
subcarriers in the time direction. Specifically, the reception quality is calculated
from an error between signals obtained by equalizing the TMCC signals by use of the
channel characteristics acquired from interpolation of the channel characteristics
of the SP signals, and signals obtained by differential decoding and hard decision
of the TMCC signals. In this case, since an integrated quality signal including the
effect of deterioration due to an interpolation error is detected, high-accuracy noise
estimation can be achieved. When it is attempted to apply the noise power calculation
method described in PTL 2 to the DVB-T2, by using the CP signals in place of the TMCC
signals, the symbol including the CP signals can be assessed. However, the symbol
including no CP signal cannot be assessed by the same method.
[0032] An impulse interference environment is one of reception environments in which the
state of the reception channel is hard to be reflected on the reliability information.
The impulse interference is an irregular and random interference signal, and occurs
in an impulse manner from power-ON/OFF of household electrical appliances, lighting
equipment, or automobile ignition.
[0033] In OFDM decoding, the impulse interference is diffused into a wider frequency band
by the FFT, thereby degrading the reception performance. The noise power locally increases
in the symbol in which the interference wave exists. For this reason, when the noise
power is averaged among the symbols for improving the accuracy of the noise power
of the reliability information, in the symbol in which the impulse interference exists,
an error occurs between the reliability information and the actual transmission environment.
[0034] According to a method of reducing such effect of the impulse interference environment,
the reception performance is improved by eliminating a signal having an integrated
level higher than a predetermined level. In this case, since an impulse interference
component having a high reception level is eliminated, the impulse interference signal
itself does not exist. However, the desired OFDM signal itself also disappears by
eliminating the received signal to disappear, while a noise component generated with
the elimination still remains. Thus, an error occurs between the reliability information
obtained by equalizing the noise power among the symbols and the noise power in the
symbol including the noise component remaining with the elimination, resulting in
that the LDPC decoding performance cannot be used to the fullest extent.
[0035] Thus, for example, PTL 1 describes an effective method of eliminating such local
difference in the reliability information of the symbols to improve the accuracy.
According to the method described in PTL 1, for the noise power calculated from the
pilot signal or an OFDM band spectrum, average noise power in a symbol direction is
compared with noise power in each symbol, and in the case where the noise power in
each symbol exceeds a predetermined threshold, it is determined that impulse interference
exists, and a value of the noise power in each symbol is used to generate the reliability
information. On the contrary, in the case where the noise power in each symbol does
not exceed the predetermined threshold, it is determined that the impulse interference
does not exist, and a value of the averaged noise power in the symbol direction is
used to generate the reliability information. Thereby, even when the noise power is
locally increased by the existence of the impulse interference or the elimination
of the signal, the noise power can be correctly found. By generating high-accuracy
reliability information in this manner, the LDPC decoding performance can be improved.
[0036] However, PTL 1 fails to disclose a specific method of calculating the noise power
in units of symbol.
[0037] When it is attempted to apply the high-accuracy noise power calculation method in
units of symbol, which is described in PTL 2, to the DVB-T2 scheme, as described above,
by using the CP signals in place of the TMCC signals, the noise power of the frame
including the CP signals can be calculated. However, in the DVB-T2 frame according
to the DVB-T2 scheme, the CP signals are not arranged in the P2 symbol and the Frame
Close symbol. In such symbols including no CP signal, the noise power cannot be calculated
based on the CP signals and therefore, the average noise power in the symbol direction
needs to be used in these symbols. As a result, when the impulse interference or signal
elimination occurs in the symbols in which the noise power cannot be calculated in
the units of symbol according to the conventional art, for example, because the CP
signals are not arranged, a difference between the actual noise power of the current
symbol and the average noise power of the current symbol and other symbols is generated,
thereby lowering the accuracy of the reliability information used for the LDPC decoding
to degrades the reception performance.
[0038] To solve the above problem, a receiver according to one aspect of the present invention
is a receiver including: a demodulator that demodulates a modulation wave modulated
according to orthogonal frequency division multiplexing (OFDM), the demodulator including:
an interference wave detector that detects that a received modulation wave which is
received by the receiver includes an interference wave when received power of each
sample of the received modulation wave exceeds a threshold, and upon the detection,
executes replacement processing of replacing a received signal exceeding the threshold
with a predetermined value; a first interference wave power estimation unit configured
to estimate interference wave power included in an OFDM symbol included in the received
modulation wave on the basis of the number of samples that have been subjected to
the replacement processing in the OFDM symbol; and a demodulated data generator that
demodulates the received modulation wave by executing demodulation processing of demodulating
the received modulation wave that has been subjected to the replacement processing
by the interference wave detector on the basis of the interference wave power estimated
by the first interference wave power estimation unit, to generate demodulation data.
[0039] Thus, the receiver calculates the interference wave power included in the OFDM symbol
on the basis of the number of samples in which the received power exceeds the predetermined
threshold in the OFDM symbol, thereby enabling estimation of the interference wave
power in units of the OFDM symbol without depending on the type of signal transmitted
in the OFDM symbol. As a result, in the demodulation processing, the interference
wave power calculated on the basis of the number of samples in which the received
power exceeds the predetermined threshold can be used as the interference wave power
of the OFDM symbol including no CP signal, even when impulse interference or signal
elimination exists in the OFDM symbol including no CP signal, stable reception can
be achieved.
[0040] That is, according to the conventional noise power detection method using the CP
signals included in the OFDM symbol, the interference wave power of the OFDM symbol
including particular signals can be estimated by using the particular signals. On
the contrary, according to the present invention, the interference wave power in units
of OFDM symbol can be estimated without depending on the type of signal transmitted
in the OFDM symbol.
[0041] For example, the demodulated data generator may include a reliability estimation
unit configured to estimate reliability information with respect to the received modulation
wave to obtain a lower reliability of the OFDM symbol as the interference wave power
estimated by the first interference wave power estimation unit is larger; and an error
correction unit configured to execute error correction processing of correcting an
error included in the received modulation wave on the basis of the reliability information
estimated by the reliability estimation unit, as the demodulation processing for the
received modulation wave, to generate the demodulation data for the received modulation
wave.
[0042] Thus, in the demodulation processing, whether or not noise in the symbol can be estimated
according to the noise power detection method using the CP signals, noise power taking
into account the estimated interference power can be estimated. As a result, even
when impulse interference or signal elimination exists, error correction can be performed
based on the high-accuracy reliability information, thereby enabling stable reception.
[0043] For example, the error correction unit may be configured to execute weighting processing
of a log likelihood ratio in LDPC (Low Density Parity Check) demodulation on the basis
of the reliability information estimated by the reliability estimation unit, as the
demodulation processing for the received modulation wave, to generate demodulation
data for the received modulation wave.
[0044] Thus, the LDPC (Low Density Parity Check) demodulation processing can be executed
based on the high-accuracy reliability information. In the LDPC demodulation processing,
the inputted reliability information can be taken into account, and by inputting the
high-accuracy reliability information, higher-accuracy demodulation processing can
be achieved.
[0045] For example, the demodulated data generator may include: an FFT (Fast Fourier Transform)
window position detector that identifies a start timing of the OFDM symbol included
in the received modulation wave; and an FFT unit configured to apply FFT processing
to the received modulation wave on the basis of the start timing of the OFDM symbol,
which is identified by the FFT window position detector, and applies the demodulation
processing to the received modulation wave that has been subjected to the FFT processing,
to generate the demodulation data.
[0046] Thus, impulse interference or signal elimination that exists during the actually
Fourier-transformed symbol period can be estimated.
[0047] For example, the interference wave detector may execute, as the replacement processing,
processing of replacing the received signal exceeding the threshold with 0 as the
predetermined value.
[0048] Thus, by setting the sample having the interference wave to 0, residues of the interference
power can be reduced, thereby enabling stable reception.
[0049] For example, the interference wave detector may execute processing of replacing the
received signal exceeding the threshold with the threshold as the predetermined value.
[0050] Thus, by setting the sample having the interference wave to the predetermined value,
residues of the interference power can be reduced.
[0051] For example, the demodulator further may include a second interference wave power
estimation unit configured to estimate interference wave power included in a first
OFDM symbol included in the received modulation wave on the basis of interference
wave power included in a second OFDM symbol that is different from the first OFDM
symbol and magnitude of an effect on the first OFDM symbol, which is brought by the
interference wave power included in the second OFDM symbol, and the demodulated data
generator applies demodulation processing including error correction taking into account
the interference wave power estimated by the first interference wave power estimation
unit to a first OFDM symbol group having at least one OFDM symbol included in the
received modulation wave to generate demodulation data for the received modulation
wave, and applies demodulation processing including error correction taking into account
the interference wave power estimated by the second interference wave power estimation
unit to a second OFDM symbol group having an OFDM symbol that is the OFDM symbol included
in the received modulation wave other than the OFDM symbol of the first OFDM symbol
group, to generate the demodulation data for the received modulation wave.
[0052] Thus, the interference wave power can be calculated according to the proper interference
wave power method selected from the plurality of interference wave power estimation
methods for each symbol, and the calculated interference wave power can be used in
the demodulation processing to achieve effective demodulation, thereby enabling stable
reception.
[0053] For example, the receiver may receive an airwave based on a Digital Video Broadcasting-Terrestrial
2 (DVB-T2) scheme as the modulation wave, and the demodulated data generator may use
an OFDM symbol group including no OFDM symbol having a CP (Continual Pilot) signal
as the first OFDM symbol group, to generate the demodulation data for the received
modulation wave.
[0054] Thus, by calculating the interference power on the basis of the number of samples
exceeding the predetermined threshold during the OFDM symbol period, the interference
power can be calculated in even the symbol, to which the processing using the CP signals
can be applied, and the calculated interference power can be used in the demodulation
processing to achieve effective demodulation, thereby enabling stable reception.
[0055] For example, the demodulated data generator may use an OFDM symbol group including
an OFDM symbol having a P2 symbol or an FC (Frame Close) symbol according to the DVB-T2
scheme as the first OFDM symbol group, to generate the demodulation data for the received
modulation wave.
[0056] Thus, by calculating the interference power on the basis of the number of samples
exceeding the predetermined threshold during the OFDM symbol period, the interference
power can be calculated in even the P2 symbol or the FC symbol, to which the processing
using the CP signals can be applied, and the calculated interference power can be
used in the demodulation processing to achieve effective demodulation, thereby enabling
stable reception.
[0057] For example, the demodulated data generator may further include a channel estimation
unit configured to estimate channel characteristics of the modulation wave on the
basis of the interference wave power estimated by the first interference wave power
estimation unit, and the demodulated data generator may demodulate the received modulation
wave by executing demodulation processing based on the channel characteristicss estimated
by the channel estimation unit, to generate the demodulation data.
[0058] Thus, by calculating the interference power on the basis of the number of samples
exceeding the predetermined threshold during the OFDM symbol period, the interference
power can be calculated whether or not noise in the symbol can be estimated, and the
calculated interference power can be used to achieve effective channel estimation,
thereby enabling stable reception.
[0059] For example, the channel estimation unit may include a plurality of different channel
estimation interpolation units that perform mutually different methods of interpolating
the channel characteristicss, the first interference wave power estimation unit may
be configured to estimate interference power corresponding to each of the channel
estimation interpolation units, and the channel estimation unit may be configured
to output one of outputs from the plurality of channel estimation interpolation units
as the channel characteristicss on the basis of the interference power estimated by
the first interference wave power estimation unit.
[0060] Thus, by calculating the interference power on the basis of the number of samples
exceeding the predetermined threshold during the OFDM symbol period, the interference
power can be calculated whether or not noise in the symbol can be estimated, and the
calculated interference power can be used to achieve effective channel estimation,
thereby enabling stable reception.
[0061] For example, the first interference wave power estimation unit may be configured
to calculate interference wave power included in the OFDM symbol included in the received
modulation wave, using the number of samples that have been subjected to the replacement
processing in the OFDM symbol, the number of FFT samples in the OFDM symbol, and a
predetermined coefficient.
[0062] Thus, the interference power can be calculated based on the number of samples exceeding
the predetermined threshold during the OFDM symbol period, the number of FFT samples,
and the predetermined coefficient with high accuracy, and the calculated interference
power can be used to achieve effective demodulation, thereby enabling stable reception.
[0063] For example, the demodulated data generator may further include a channel estimation
unit configured to estimate a channel characteristic of each carrier included in a
fourth OFDM symbol disposed before or after a third OFDM symbol included in the received
modulation wave by interpolation using channel characteristicss calculated using a
pilot signal included in the third OFDM symbol, an equalizer configured to execute
equalization processing of correcting a signal of the fourth OFDM symbol on the basis
of the channel characteristicss estimated by the channel estimation unit, an error
correction unit configured to perform error correction for the signal corrected by
the equalizer on the basis of reliability information representing reliability of
the signal corrected by the equalizer, and a reliability information estimation unit
configured to estimate reliability information of the signal included in the fourth
OFDM symbol on the basis of interference wave power of the third OFDM symbol, which
is estimated by the interference wave power estimation unit.
[0064] Thus, by calculating the interference power on the basis of the number of samples
exceeding the predetermined threshold during the OFDM symbol period, the interference
power can be calculated whether or not noise in the symbol can be estimated, and the
calculated interference power can be used to achieve effective channel estimation
of other OFDM symbols, thereby enabling stable reception.
[0065] An integrated circuit according to one aspect of the present invention is an integrated
circuit including a demodulator that demodulates a modulation wave modulated according
to orthogonal frequency division multiplexing (OFDM), the demodulator including: an
interference wave detector that detects that a received modulation wave that is the
modulation wave received by the receiver includes interference wave when received
power of each sample of the received modulation wave exceeds a threshold, and upon
the detection, executes replacement processing of a replacing received signal exceeding
the threshold with a predetermined value; a first interference wave power estimation
unit configured to estimate interference wave power included in an OFDM symbol included
in the received modulation wave on the basis of the number of samples that have been
subjected to the replacement processing; and a demodulated data generator that demodulates
the received modulation wave by executing demodulation processing of demodulating
the received modulation wave that has been subjected to the replacement processing
by the interference wave detector on the basis of the interference wave power estimated
by the first interference wave power estimation unit, to generate demodulation data.
[0066] Thus, the integrated circuit has the same effect as the above-mentioned receiver.
[0067] A receiving method according to one aspect of the present invention is a receiving
method comprising demodulating a modulation wave modulated according to orthogonal
frequency division multiplexing (OFDM), wherein the demodulating includes: an interference
wave detection step of detecting that received modulation wave that is the modulation
wave received according to the receiving method includes interference wave when received
power of each sample of the received modulation wave exceeds a threshold, and upon
the detection, executing replacement processing of replacing a received signal exceeding
the threshold with a predetermined value; a first interference wave power estimation
step of estimating interference wave power included in an OFDM symbol included in
the received modulation wave on the basis of the number of samples that have been
subjected to the replacement processing; and a demodulation data generation step of
demodulating the received modulation wave by executing demodulation processing of
demodulating the received modulation wave that has been subjected to the replacement
processing in the detecting on the basis of the interference wave power estimated
in the estimating, to generate demodulation data.
[0068] Thus, the receiving method has the same effect as the above-mentioned receiver.
[0069] A program as one aspect of the present invention causes a computer to perform the
above-mentioned receiving method.
[0070] Thus, the program has the same effect as the above-mentioned receiver.
[0071] These general and specific aspects may be realized by a system, a method, an integrated
circuit, a computer program, or a recording medium, or may be realized by any combination
of a system, a method, an integrated circuit, a computer program, and a recording
medium.
[0072] Embodiments of the present invention will be described below with reference to figures.
[0073] The following embodiments are specific examples of the present invention. Values,
shape, materials, components, position and connection of the components, steps, and
the order of the steps are merely examples, and do not intend to limit the present
invention. Among components in the following embodiments, components that are not
described in independent claims defining the highest concept are described as optional
components.
(First embodiment)
[0074] First embodiment of a receiver from one aspect of the present invention will be described
below with reference to Fig. 1 to Fig. 6. The DVB-T2 scheme as the 2nd-generation
European terrestrial digital broadcasting standard is used herein as an example.
[0075] Fig. 1 is a block diagram showing a receiver 10 in First embodiment of the present
invention. The receiver 10 includes an antenna 1, a tuner 2, a demodulator 11, a decoder
3, and a display 4.
[0076] The antenna 1 receives a modulation wave modulated according to orthogonal frequency
division multiplexing (OFDM). Airwave based on the DVB-T2 scheme is an example of
the modulation wave modulated according to the orthogonal frequency division multiplexing
(OFDM).
[0077] The tuner 2 selects a received signal of a desired reception channel from the modulation
wave received by the antenna 1.
[0078] The demodulator 11 demodulates the received analog signal selected by the tuner
2.
[0079] The decoder 3 decodes the signal that is demodulated by the demodulator 11 and compressed
according to the H.264 or the like.
[0080] The display 4 outputs video/voice decoded by the decoder 3.
[0081] Fig. 2 is a block diagram showing a configuration of the demodulator 11 in accordance
with First embodiment. The demodulator 11 includes an A/D converter 101, an interference
wave detector 102, an interference wave power estimation unit 104, and a demodulated
data generator 12. The demodulated data generator 12 includes a time axis processor
103, an FFT unit 105, a channel estimation unit 106, equalizer 107, reliability estimation
unit 108, and an error correction unit 109.
[0082] The A/D converter 101 converts the analog output signal from the tuner 2 into a digital
signal, and outputs the digital signal to the interference wave detector 102.
[0083] The interference wave detector 102 detects an interference wave contained in the
received signal converted into the digital signal by the A/D converter 101 and outputs
a detection result to the interference wave power estimation unit 104 as well as converts
the received signal (sample) containing the detected interference wave into a predetermined
value and outputs the predetermined value to the time axis processor 103. Specific
processing will be described later.
[0084] The time axis processor 103 determines a start time position of FFT processing during
the OFDM symbol period (hereinafter referred to as FFT window position) for the output
signal of the interference wave detector 102, outputs the start time position to the
FFT unit 105, and outputs the FFT window position information to the interference
wave power estimation unit 104.
[0085] The interference wave power estimation unit 104 estimates interference power on the
basis of the received signal that has been subjected to the interference wave processing
by the interference wave detector 102 and the FFT window position information determined
by the time axis processor 103. The interference wave power estimation unit 104 corresponds
to the first interference wave power estimation unit. Specific processing performed
by the interference wave power estimation unit 104 will be described later.
[0086] The FFT unit 105 Fourier-transforms the output signal from the time axis processor
103 into a signal along the frequency axis on the basis of an FFT window position
signal, and outputs the Fourier-transformed signal to the channel estimation unit
106 and the equalizer 107.
[0087] The channel estimation unit 106 interpolates channel characteristics obtained by
dividing the SP signals contained in the signal Fourier-transformed according to FFT
by known SP signals, thereby estimating the channel characteristicss in all subcarriers,
and outputs the estimated channel characteristics to the equalizer 107 and the reliability
estimation unit 108.
[0088] The equalizer 107 corrects phase and amplitude distortion of the output signal from
the FFT unit 105, which is generated in the channel, on the basis of the channel characteristics
estimated by the channel estimation unit 106.
[0089] The reliability estimation unit 108 finds the noise power on the basis of a channel
estimated value estimated by the channel estimation unit 106 and the interference
power estimated by the interference wave power estimation unit 104, and generates
reliability information to be used in the error correction unit 109 from the noise
power.
[0090] The error correction unit 109 corrects an error of the signal corrected by the equalizer
107 on the basis of the reliability information estimated by the reliability estimation
unit 108.
[0091] Fig. 3A is a view showing a configuration of the interference wave detector 102.
Fig. 3B shows an example of an interference wave detection signal.
[0092] As shown in Fig. 3A, the interference wave detector 102 includes an interference
wave sample detector 111 and a mask processor 112.
[0093] The interference wave sample detector 111 compares the received signal ((a) in Fig.
3B) converted into the digital signal by the A/D converter 101 with a predetermined
threshold, generates a signal representing a sample position exceeding the threshold
value, and outputs the signal representing the sample position together with the received
signal to the mask processor 112. A following interference wave detection signal (Interference
Exist) ((b) in Fig. 3B) can be used as the signal representing the sample position
exceeding the threshold value. That is, for the sample having the received signal
level (received power) exceeding the threshold level, the interference wave detection
signal outputs Interference Exist = 1 (interference wave exists). For the sample having
the received signal level that does not exceed the threshold level, the interference
wave detection signal outputs Interference Exist = 0 (interference wave does not exist).
That the received signal level exceeds the threshold includes both cases of positive
sign and negative sign. That is, that a threshold T
h is larger than 0 includes the cases where the positive (> 0) received signal level
is larger than the threshold T
h and where the negative (< 0) received signal level is smaller than the negative threshold
(-T
h).
[0094] In the sample of Interference Exist= 1 (interference wave exists) as a detection
result of the interference wave, the mask processor 112 replaces the received signal
with 0 ((c) in Fig. 3B), and outputs 0 together with the interference wave detection
signal to the time axis processor 103 and the interference wave power estimation unit
104.
[0095] Fig. 4 shows a configuration of the time axis processor 103. The time axis processor
103 includes a synchronizer 121 and an FFT window position detector 122. The synchronizer
121 frequency-converts an output signal from the interference wave detector 102 into
a baseband signal, synchronizes the carrier frequency with the sampling frequency,
and outputs the baseband signal to the FFT window position detector 122. For Fourier
transformation of the time axis signal, the FFT window position detector 122 determines
the FFT window position of the OFDM symbol, and outputs the FFT window position to
the FFT unit 105 and the interference wave power estimation unit 104.
[0096] Fig. 5 shows a configuration of the interference wave power estimation unit 104.
The interference wave power estimation unit 104 includes an interference wave sample
counter 131 and an interference power converter 132.
[0097] For the interference wave detection signal detected by the interference wave detector
102, the interference wave sample counter 131 outputs the number of samples determined
as "interference wave exists" in the OFDM symbol section during which the FFT processing
is executed, by using the FFT window position information detected by the FFT window
position detector 122, to the interference power converter 132.
[0098] Using the number of samples of "interference wave exists" in the OFDM symbol section,
which is counted by the interference wave sample counter 131, the interference power
converter 132 estimates interference power existing in the OFDM symbol, and outputs
the estimated interference power to the reliability estimation unit 108. Detailed
operations of each unit will be sequentially described.
[0099] Since the interference wave detector 102 performs the masking processing of replacing
the received signal level of the samples of "interference wave exists" with 0, the
number of interference wave samples is equal to noise amount increased by eliminating
the OFDM signal. For this reason, given that the OFDM signal power is P
OFDM, the signal level of each sample of the OFDM signal becomes P
OFDM/N
FFT. Thus, when the noise amount increased in the OFDM symbol is defined as I
mask on the basis of the number of samples N
I of the "interference wave exists" included in the OFDM symbol, I
mask can be expressed by (Equation 1).

[0100] The interference power converter 132 estimates the noise amount increased in each
OFDM symbol according to the conversion formula (Equation 1), and outputs the estimated
noise amount to the reliability estimation unit 108, thereby increasing the accuracy
of the reliability information to improve the reception performance.
[0101] Fig. 6 is a view showing a configuration of the reliability estimation unit 108.
The reliability estimation unit 108 shown in Fig. 6 includes a noise estimation unit
141, an interference power adder 142, and a reliability information converter 143.
[0102] From the Fast-Fourier-Transformed signal, the channel characteristics estimated by
the channel estimation unit 106, and known CP signal, the noise estimation unit 141
estimates an average noise power value among the OFDM symbols (average noise power
among the symbols) on the basis of the received CP signal.
[0103] The interference power adder 142 adds the interference power estimated by the interference
wave power estimation unit 104 to the estimated average noise power value among the
symbols, and outputs the noise power for each symbol taking into account the effect
of the interference wave.
[0104] The reliability information converter 143 estimates the reliability information to
be used for LDPC decoding on the basis of the OFDM signal power based on the channel
characteristics, which is estimated by the channel estimation unit 106, and the noise
power calculated by the interference power adder 142, and outputs the reliability
information to the error correction unit 109 to achieve effective error correction.
[0105] To estimate noise in the noise estimation unit 141, for example, the configuration
described in PTL 1, in which the TMCC signals are replaced with the CP signals, is
adopted. Specifically, a known CP signal X
CP is compared with a received signal Y
CP equalized using the channel characteristics H
CP obtained through channel estimation by interpolation of the SP signals, and uses
its error amount as the noise power of the CP signals representing the noise amount
of the OFDM symbol. Since the noise amount is calculated from some signals (CP signals),
to improve the estimation accuracy with respect to thermal noise component, average
noise power among symbols N
ACC accumulated over some symbols is used.
[0106] In the case where the time axis processor 103 performs processing of converting A/D
conversion sampling rate into OFDM signal sampling rate (rate conversion), in consideration
of rate conversion of the received signal, the interference wave power estimation
unit 104 may also process sample timing of the interference wave detection signal.
Further, based on a signal after rate conversion, the interference detection and processing
of the interference detection sample by the interference wave detector 102 (processing
of converting into 0) may be performed. In this case, an interference detection signal
need not allow for the effect of rate conversion.
[0107] Although the mask processor 112 replaces the received signal with 0 on the basis
of the signal detected by the interference wave sample detector 111 in this embodiment,
batch processing may be performed such that the sample exceeding the threshold is
replaced with 0 to output a detection signal.
[0108] The reliability information converter 143 may convert the reliability information
by using information other than the noise power and the signal power. For example,
by using a frequency-varying component that occurs with the Doppler frequency, the
reliability information corresponding to frequency variance can be estimated.
[0109] The number of samples included in the OFDM symbol, which is calculated by the interference
wave sample counter 131, represents the noise amount locally increased by eliminating
the OFDM signal in the symbol. For this reason, the number of interference wave samples
may be used as a signal representing that the interference wave exists in various
blocks. For example, in the calculation of the average noise amount among symbols
in the noise estimation unit 141, the noise amount of the symbol exceeding the predetermined
number of interference wave samples may be eliminated in averaging processing.
[0110] Although one aspect of the present invention is applied to the error correction method
or demodulation method using the LDPC in this embodiment, it can be applied to other
error correction methods or demodulation methods.
[0111] As described above, the receiver in accordance with one aspect of the present invention
can calculate the interference wave power in the OFDM symbol on the basis of the number
of samples having the received power exceeding the predetermined threshold in the
OFDM symbol, thereby estimating the interference wave power in units of OFDM symbol
without depending on the type of the signal transmitted in the OFDM symbol. As a result,
in the demodulation processing, the interference wave power calculated based on the
number of samples having the received power exceeding the predetermined threshold
can be used as the interference wave power of the OFDM symbol including no CP signal.
Thus, even when impulse interference or signal elimination exists in the OFDM symbol
including no CP signal, stable reception can be achieved.
[0112] That is, conventionally, as in the noise power detection method using the CP signals
included in the OFDM symbol, the interference wave power of the OFDM symbol including
particular signals can be estimated by using the particular signals. On the contrary,
according to the present invention, the interference wave power can be estimated in
the units of OFDM symbol without depending on the type of signal transmitted in the
OFDM symbol.
[0113] In the demodulation processing, for example, whether or not noise in the symbol can
be estimated according to the noise power detection method using the CP signals, the
noise power taking into account the estimated interference power can be estimated
to generate the reliability information. Therefore, even when impulse interference
or signal elimination exists, error correction can be performed based on the high-accuracy
reliability information, thereby enabling stable reception.
[0114] The LDPC (Low Density Parity Check) demodulation processing can be performed on the
basis of the high-accuracy reliability information. LDPC demodulation processing enables
demodulation processing taking into account the inputted reliability information,
and realizes demodulation processing with higher accuracy by inputting the high-accuracy
reliability information.
[0115] Impulse interference or signal elimination that exists during the actually Fourier-transformed
symbol period can be estimated.
[0116] By setting the sample having the interference wave to 0, residues of interference
power can be reduced, thereby enabling stable reception.
[0117] By calculating the interference power on the basis of the number of samples exceeding
the predetermined threshold during the OFDM symbol period, the interference power
can be calculated whether or not noise in the symbol can be estimated. Then, effective
channel estimation can be achieved based on the calculated interference power, thereby
enabling stable reception.
[0118] Based on the number of samples exceeding the predetermined threshold during the OFDM
symbol period and a coefficient related to a predetermined constant, the interference
power can be calculated with high accuracy, and effective demodulation can be achieved
on the basis of the calculated interference power, thereby enabling stable reception.
(Second embodiment)
[0119] A receiver in accordance with Second embodiment of the present invention will be
described below with reference to Fig. 7 to Fig. 10. The same components as those
in Fig. 1 to Fig. 6 are given the same reference numerals and description thereof
is omitted.
[0120] Fig. 7 is a block diagram showing a receiver 20 in accordance with Second embodiment
of the present invention, and Fig. 8 is a block diagram showing a configuration of
a demodulator 21. Fig. 8 is different from Fig. 2 only in an interference wave detector
202 and an interference wave power estimation unit 204.
[0121] Fig. 9 is a view showing a configuration of the interference wave detector 202. The
interference wave detector 202 includes an interference wave sample detector 211 and
a clip processor 212.
[0122] Like the interference wave sample detector 111 in First embodiment, the interference
wave sample detector 211 compares a received signal converted into a digital signal
by an A/D converter with a predetermined threshold, and outputs an interference wave
detection signal together with the received signal.
[0123] In the sample of Interference Exist= 1 (interference wave exists) as a detection
result of the interference wave, the clip processor 212 replaces the received signal
with a predetermined value. The predetermined value may be the same as the threshold
in the interference wave sample detector 211. When the received signal exceeds the
negative threshold, the predetermined value may be same as the negative threshold
in this processing.
[0124] The interference wave detector 202 outputs the interference wave detection signal
to the interference wave power estimation unit 204. Fig. 10 is a block diagram showing
a configuration of the interference wave power estimation unit 204. The interference
wave power estimation unit 204 includes an interference wave sample counter 131 and
an interference power converter 232.
[0125] As in First embodiment, the interference wave sample counter 131 counts the number
of samples determined as "interference wave exists", which are included in the OFDM
symbol, and outputs the count to the interference power converter 232.
[0126] Based on the number of samples determined as "interference wave exists", which is
calculated by the interference wave sample counter 131, the interference power converter
232 calculates the interference wave power included in the OFDM signal. In this embodiment,
since the interference wave is converted into the predetermined value (clip processing),
it can be deemed that the interference wave corresponding to the predetermined value
for the number of interference wave samples exists in the OFDM symbol. Given that
the OFDM signal power is P
OFDM and the square of the interference wave clipped value is A
Clip x P
OFDM, the signal level of each sample of the OFDM signal becomes P
OFDM/N
FFT, while the signal level of the clipped interference wave power becomes A
Clip X P
OFDM/N
FFT. Consequently, interference wave power I
Clip at clipping of the interference wave can be expressed by (Equation 2).

[0127] As in First embodiment, the interference power adder 142 of the reliability estimation
unit 108 takes into account the interference wave component included in the symbol
to increase the accuracy of the reliability information to be used for LDPC decoding
in the reliability estimation unit, thereby enabling stable reception.
[0128] When the time axis processor 103 performs processing of converting A/D conversion
sampling rate into OFDM signal sampling rate (rate conversion), in consideration of
the rate conversion of the received signal, the interference wave power estimation
unit 104 may also process sample timing of the interference wave detection signal.
Further, based on a signal after rate conversion, the interference detection and processing
of the interference detection sample by the interference wave detector 202 (processing
of converting into the predetermined value) may be performed. In this case, an interference
detection signal need not allow for the effect of rate conversion.
[0129] Although the clip processor 212 performs conversion into the predetermined value
on the basis of the signal detected by the interference wave sample detector 211,
batch processing may be performed such that the sample exceeding the threshold is
replaced with the predetermined value to output a detection signal.
[0130] Since the interference power in the sample determined as "interference wave exists"
in Equation 2 includes the OFDM signal itself to be exact, the OFDM signal component
may be subtracted.
[0131] As described above, in the receiver according to one aspect of the present invention,
by replacing the sample having the interference wave with the predetermined value,
residues of the interference power can be reduced, thereby enabling stable reception.
(Third embodiment)
[0132] A receiver in accordance with Third embodiment of the present invention will be described
below with reference to Fig. 11 to Fig. 14A. The same components as those in Fig.
1 to Fig. 6 are given the same reference numerals and description thereof is omitted.
[0133] Fig. 11 is a block diagram showing a receiver 30 in accordance with Third embodiment
of the present invention, and Fig. 12 is a block diagram showing a configuration of
a demodulator 31. The demodulator 31 shown in Fig. 12 is different from the demodulator
11 in First embodiment in a configuration of an interference wave power estimation
unit 304.
[0134] Fig. 13 is a view showing the configuration of the interference wave power estimation
unit 304. The interference wave power estimation unit 304 includes an interference
wave sample counter 131, an interference power converter 132, a second interference
power converter 332, and an adder 333. The interference wave power estimation unit
304 corresponds to a second interference wave power estimation unit.
[0135] As in First embodiment, the interference wave sample counter 131 counts the number
of samples determined as "interference wave exists" in the OFDM symbol on the basis
of the interference wave detection signal detected by the interference wave detector
102 and the OFDM symbol position detected by the FFT window position detector 122,
at which the FFT is performed, and outputs the count to the interference power converter
132 and the second interference power converter 332.
[0136] As in First embodiment, the interference power converter 132 calculates the interference
power included in the received OFDM symbol from the output of the interference wave
sample counter 131. This embodiment is different from First embodiment in the second
interference power converter 332.
[0137] The second interference power converter 332 calculates the interference power occurring
in the current OFDM symbol from the interference wave including other OFDM symbols.
Here, considering that, through interpolation processing in channel estimation, the
effect of the interference wave is spread to the other OFDM symbols corrected by the
equalizer 107, the interference wave power is estimated by the channel estimation.
[0138] The adder 333 adds the interference power of the current OFDM symbol estimated by
the interference power converter 132 and the interference power of the other OFDM
symbols estimated by the second interference power converter 332 and outputs the sum.
[0139] Estimation of the channel characteristics is to obtain the channel characteristicss
of all subcarriers by interpolating the channel characteristicss of the SP signals,
the P2 pilot signals, and the FC signals that exist in a distributed manner in the
time axis (symbol) direction and the frequency axis (carrier) direction. Interpolation
methods include (A) a method of interpolating the signals in the time axis (symbol)
direction and then, interpolating the signals in the frequency axis (carrier) direction,
and (B) a method of interpolating the signals only in the frequency axis (carrier)
direction.
[0140] Fig. 14A shows a transition of CNR (Carrier to Noise ratio) of each OFDM symbol corrected
by the equalizer 107 in each of cases where as the interpolation processing in the
channel estimation in an impulse interference environment, (A) time axis interpolation
and frequency interpolation are used, and (B) only the frequency axis interpolation
is used (no time axis interpolation). A horizontal axis represents the symbol direction
(time direction), and a vertical axis represents the CNR. When the impulse interference
occurs at timings expressed by asterisk (*), (B) in the case where only the frequency
axis interpolation is used, the CNR lowers only in the symbols having the impulse
interference, and (A) in the case where the time axis interpolation is also used,
since the symbol having the impulse interference is used in the interpolation processing,
an interpolation error occurs due to the interference wave and therefore, the CNR
lowers also in the symbols before and after the symbol having the impulse interference.
[0141] In consideration of this, in this embodiment, the second interference power converter
332 takes into account of the effect of the interference wave in the channel estimation,
and in the case of (B) only the frequency axis interpolation, the effect of the current
symbol on the channel characteristics is regarded as the interference power. In the
case of (A) time axis interpolation + frequency interpolation, the effect of the symbol
having interference and the symbols before and after the current symbol is also regarded
as the interference power. Here, the number of interference wave samples, which is
outputted from the interference wave sample counter 131, is subjected to the same
processing as time interpolation, the number of interference samples that takes into
account the effect of the interference wave by time axis interpolation is estimated,
and the interference power including the interpolation error is calculated.
[0142] As described above, the effect of the interference wave on the channel estimation
changes depending on the patterns (A) time axis interpolation + frequency axis interpolation,
and (B) only frequency axis interpolation. Details of each pattern will be described
below.
((A) Time axis interpolation + frequency axis interpolation)
[0143] The DVB-T2 scheme has eight types of SP patterns. For simplifying description, linear
interpolation in the time axis direction is used as an example. An SP carrier interval
in the time axis direction is classified into two types: (1) every two carriers and
(2) every four carriers. Thus, the range in which the effect of the interference wave
in the time interpolation is spread is one symbol in the case (1) and three symbols
in the case (2) before and after the symbol having the detected interference wave.
As a result, the number of interference wave samples for estimating the channel estimation
error in the i symbol due to the interference wave: (1) N
H_TF2sym and (2) N
H_TF4sym are as follows.

((B) Frequency axis interpolation)
[0144] In the case of only the frequency axis interpolation, since the effect is not spread
to symbols before and after the rear of the symbol having the interference wave, the
number of interference wave samples in the i symbol in the channel estimation: N
H_F(i) is as follows.

[0145] To calculate the interference power taking into account the channel estimation error
on the basis of the number of interference wave samples according to each of the above-mentioned
interpolation methods, it is required to correct the noise amount related to SP signal
power and interpolation filter band. The interference power taking into account the
channel estimation error in the cases (A) and (B) is as represented by (Equation 6)
and (Equation 7), respectively. It is assumed that A
SP is boost of the SP signal, BWT is band of the time interpolation filter, and BWF
is band of the frequency interpolation filter.
(A)

(B)

[0146] The adder 333 adds the interference power estimated by the interference wave power
estimation unit to the interference power taking into account the channel estimation
error corresponding to respective interpolation method, thereby reflecting the interference
power included in the OFDM symbol as well as the interference power including the
effect of the interference wave in the channel estimation. Since the interference
power can be appropriately reflected on the reliability information in the interference
power adder 142 of the reliability estimation unit 108, high-accuracy reliability
information can be obtained, resulting in effective LDPC decoding and improvement
of the reception performance.
[0147] Although the adder 333 adds the interference power from the interference power converter
132 to the interference power from the second interference power converter 332 in
this embodiment, the adder 333 may use the interference power from either of the converters.
[0148] Although the linear interpolation is adopted as the time axis interpolation, the
linear interpolation is not limited to this, and any interpolation method (interpolation
coefficient) may be adopted.
[0149] Alternatively, as shown in Fig. 14A, considering that the effect of the interference
power varies according to the interpolation method, and the signal quality varies
in the first place, the interpolation method may be selected based on the calculated
interference power. Specifically, a channel estimation unit 206 shown in Fig. 14B
may be used. The channel estimation unit 206 includes a first channel interpolation
unit 206A, a second channel interpolation unit 206B, and a selector 206S. The first
channel interpolation unit 206A and the second channel interpolation unit 206B estimate
different channel characteristicss. The selector 206S selects either an output from
the first channel interpolation unit 206A or an output from the second channel interpolation
unit 206B, as the channel characteristics. In this manner, the reliability information
in the demodulation processing can be selected from a plurality of channel characteristicss.
Since one of the outputs from the plurality of channel interpolation units is selected,
the interference wave power estimation unit can estimate the interference power corresponding
to each interpolation processing.
[0150] Although the sample having interference is masked to 0 in this embodiment unlike
First embodiment, as in Second embodiment, the sample having interference may be replaced
with the predetermined value may be taken into account in (Equation 3) to (Equation
5).
[0151] As described above, the receiver in accordance with one aspect of the present invention
can calculate the interference wave power according to the appropriate interference
wave power estimation method selected the plurality of interference wave power estimation
methods for each symbol to use the interference wave poser in the demodulation processing,
and achieve effective decoding by using the interference wave power, thereby enabling
stable reception.
[0152] By calculating the interference power on the basis of the number of samples exceeding
the predetermined threshold during the OFDM symbol period, the interference power
of the symbols that cannot be subjected to the processing using the CP signals can
be calculated. The demodulation processing can be performed using the calculated interference
power to achieve effective demodulation, thereby enabling stable reception.
[0153] By calculating the interference power on the basis of the number of samples exceeding
the predetermined threshold during the OFDM symbol period, the interference power
of the P2 symbol and the FC symbol that cannot be subjected to the processing using
the CP signals can be calculated. The demodulation processing can be performed using
the calculated interference power to achieve effective demodulation, thereby enabling
stable reception.
[0154] By calculating the interference power on the basis of the number of samples exceeding
the predetermined threshold during the OFDM symbol period, the interference power
can be calculated whether or not noise in the symbol can be estimated, and the interpolation
method for effective channel estimation can be selected based on the interference
power, thereby enabling stable reception.
(Fourth embodiment)
[0155] A receiver in accordance with Fourth embodiment of the present invention will be
described below. The same components as those in Fig. 1 to Fig. 6 are given the same
reference numerals and description thereof is omitted.
[0156] Fig. 15 is a block diagram showing a receiver 40 in accordance with Fourth embodiment
of the present invention, and Fig. 16 is a block diagram showing a configuration of
a demodulator 41. The demodulator 41 is different from the demodulator 11 in First
embodiment in addition of the interference power in a reliability estimation unit
408.
[0157] Fig. 17 is a block diagram showing a configuration of the reliability estimation
unit 408. The reliability estimation unit 408 includes a noise estimation unit 441,
an interference power adder 442, and a reliability information converter 143. The
noise estimation unit 441 outputs an average symbol noise estimated value averaged
in the symbol direction together with non-average noise estimated value for each symbol
to the interference power adder 442.
[0158] The interference power adder 442 is different from the interference power adder 142
in First embodiment in that whether or not the interference power estimated by the
interference wave power estimation unit 104 is added is selected according to the
symbol to be processed. Here, using transmission parameter information obtained by
decoding the P2 symbol or the symbol number of the received signal using the P1 signal
as a reference, according to the type of the current symbol (P1 symbol, P2 symbol,
data symbol, or FC symbol), the average symbol noise estimated value with the addition
to the interference power is outputted in the case of a particular symbol, and the
non-average noise estimated value for each symbol in the symbol direction without
the addition to the interference power is outputted in the case of the symbols other
than the particular symbol. A specific example in the DVB-T2 scheme will be described
below.
[0159] Since the P2 symbol and the FC symbol do not include the CP signal according to the
DVB-T2 scheme, in these symbols, noise power cannot be estimated by using the CP signal.
On the contrary, in the other symbols, noise power can be estimated by using the CP
signal for each symbol. Thus, in the P2 symbol or the FC symbol, in which noise power
cannot be estimated by using the CP signal for each symbol, the noise estimated value
averaged in the symbol direction with the addition to the interference power is outputted.
In the other symbols, the non-average noise estimated value for each symbol without
the addition of the symbol direction is outputted.
[0160] As described above, by using the noise estimated value calculated for each symbol
in the symbols that can estimate noise for each symbol, and adding the interference
power to the average noise estimated value in the symbols that cannot estimate noise,
the noise amount can be correctly reflected on the reliability information. For this
reason, high-accuracy reliability information can be obtained, resulting in effective
LDPC decoding and improvement of the reception performance.
[0161] In the symbols other than particular symbols such as the P2 symbol and the FC symbol,
the non-average noise estimated value for each symbol in the symbol direction is used.
However, the present invention is not limited to this, and the noise estimated value
averaged in the symbol direction or the non-average noise estimated value for each
symbol may be selected. For example, these values are compared to each other, and
when the noise estimated value for each symbol is larger, the noise estimated value
for each symbol may be used, and when the noise estimated value for each symbol is
not larger, the average noise estimated value may be used. Alternatively, when the
number of interference samples estimated by the interference wave power estimation
unit 104 is larger than a predetermined number, the noise estimated value for each
symbol may be used, and when the number of interference samples is not larger than
a predetermined number, the average noise estimated value may be used.
[0162] Although the configuration in which the necessity of addition of the interference
power is selected according to the type of symbols is applied to First embodiment,
the configuration may be applied to Second embodiment and Third embodiment.
[0163] As described above, the receiver in accordance with one aspect of the present invention
can calculate the interference power on the basis of the number of samples exceeding
the predetermined threshold during the OFDM symbol period, to calculate the interference
power whether or not noise can be estimated in the symbol, and can perform effective
channel estimation of the other OFDM symbols on the basis of the calculated interference
power, thereby enabling stable reception.
[0164] In the calculation of the interference power by the OFDM receiver in First to Fourth
embodiments, the reliability of the reliability information of the current symbol
may be decreased by a predetermined value from that of the other symbols according
to the presence/absence of the interference wave power without estimating details
of the interference wave power in (Equation 1) to (Equation 3). For example, when
the number of interference wave samples included in the OFDM symbol is equal to or
larger than the predetermined threshold, the reliability estimated value may be reduced
to half. In this case, it is not need to calculate detailed interference power, achieving
reduction of circuit size.
[0165] Each component of the OFDM receivers in accordance with First to Fourth embodiments
may be formed of an LSI as an integrated circuit. Here, the components may be individually
shaped into one chip, or may be partially or wholly integrated into one chip. Although
the LSI is mentioned herein, IC, system LSI, super LSI, or ultra LSI may be called
according to integration degree. The integrated circuit is not limited to the LSI,
may be realized by a dedicated circuit or a general processor. FPGA (Field Programmable
Gate Array) or a reconfigurable processor capable of reconfiguring connection and
setting of circuit cells in the LSI can be used. Further, if any technology for integrated
circuit in place of the LSI appears with the progress of the semiconductor technology
or other derived technology, as a matter of course, the functional blocks may be integrated
by use of the new technology. Biotechnology is one of possible technologies.
[0166] At least a part of the operational procedure of the receivers in First to Fourth
embodiments may be written into an integrated program, and for example, a CPU (Central
Processing Unit) may read and execute the program stored in a memory, or the program
may be stored in a storage medium and then, distributed.
[0167] The receivers in First to Fourth embodiments may be realized according to a receiving
method that executes at least a part of the written reception processing.
[0168] Any receiver, receiving method, integrated circuit, or program that executes a part
of the reception processing realizing First to Fourth embodiments may be combined
to realize First to Fourth embodiments. For example, a part of the configuration of
the receiver, which is described in each of the above-mentioned embodiments, may be
realized by the receiver or the integrated circuit, the operational procedure executed
by remaining parts of the configuration may be written into the reception program,
and for example, the CPU may read and execute the program stored in the memory.
[0169] Although the DVB-T2 scheme is described in First to Fourth embodiments, the present
invention is not limited to this. Like the DVB-T2, the present invention can be also
applied to the field of OFDM communication that desires improvement of the accuracy
of estimating the noise power according to change in the channel due to the interference
wave.
[0170] In each of the above-mentioned embodiments, each component may be configured of dedicated
hardware, or realized by executing a software program suitable for each component.
Alternatively, a program execution unit such as a CPU or a processor may read and
execute a software program stored in a storage medium such as a hard disc or a semiconductor
memory to realize each component. A following program is an example of software that
realizes an image decoder in each of the above-mentioned embodiments.
[0171] That is, the program causes a computer to perform a receiving method including demodulating
modulation wave modulated according to orthogonal frequency division multiplexing
(OFDM), and the demodulation step includes an interference wave detection step of
detecting that received modulation wave as the modulation wave received according
to the receiving method includes interference wave when received power of each sample
of the received modulation wave exceeds a threshold, and upon the detection, executing
replacement processing of replacing received signal exceeding the threshold with a
predetermined value, a first interference wave power estimation step of estimating
interference wave power included in an OFDM symbol included in the received modulation
wave on the basis of the number of samples that have been subjected to the replacement
processing, and a demodulation data generation step of demodulating the received modulation
wave by executing demodulation processing of demodulating the received modulation
wave that has been subjected to the replacement processing in the detecting on the
basis of the interference wave power estimated in the estimating, to generate demodulation
data.
[0172] Although the method of mounting the components according to the present invention
has been described based on the embodiment, the present invention is not limited to
the embodiment. Embodiments obtained by adding various modifications devised by those
skilled in the art to this embodiment or combining components in different embodiments
also fall within the scope of the present invention as long as they are not deviated
from the subject matter of the present invention.
[Industrial Applicability]
[0173] The receiver according to the present invention has functions of detecting the presence/absence
of the interference wave for each sample in the time axis region, estimating the interference
power on the basis of the number of samples having the interference wave during the
FFT sample period of the OFDM symbol, and estimating the reliability information used
for the LDPC decoding in consideration of the interference power, and is effective
for the OFDM receiver such as DVB-T2 requiring high-accuracy reliability information
as well as devices in wider fields such as measurement.
[Reference Signs List]
[0174]
1: antenna
2: tuner
3: decoder
4: display
10, 20, 30, 40: receiver
11, 21, 31, 41: demodulator
12, 22, 32, 42: demodulated data generator
101: A/D converter
102: interference wave detector
103: time axis processor
104: interference wave power estimation unit
105: FFT unit
106: channel estimation unit
107: equalizer
108: reliability estimation unit
109: error correction unit
111: interference wave sample detector
112: mask processor
121: synchronizer
122: FFT window position detector
131: interference wave sample counter
132: interference power converter
141: noise estimation unit
142: interference power adder
143: reliability information converter
202: interference wave detector
204: interference wave power estimation unit
211: interference wave sample detector
212: clip processor
232: interference power converter
304: interference wave power estimation unit
332: second interference power converter
333: adder
408: reliability estimation unit
441: noise estimation unit
442: interference power adder
1002: A/D converter
1003: time axis processor
1004: FFT unit
1005: channel estimation unit
1006: equalizer
1007: error correction unit
1008: reliability estimation unit